These days, power converters such as inverter circuits are employed in various types of electric apparatuses to meet requirements for power saving etc. A gate-drive system is used to turn on or off a semiconductor switching device employed in the power converter. The gate-drive system controls the semiconductor switching device by supplying a gate signal thereto to turn it on or off in response to a control signal from a control circuit. From a viewpoint of, for example, preventing malfunctions between input side circuits and output side circuits, insulation-type gate drive circuits are employed. One of such insulation-type gate drive circuits proposed includes a technology to transmit gate-drive power and gate-on/off signals in a noncontact manner by electromagnetic field resonance coupling (for example, refer to Patent Document 1).